Integrated Pest Management and Silviculture

Integrated Pest Management (IPM) is a common-sense, holistic approach to crop or forest management to minimize losses from disease and insect pests.  The general components of an IPM strategy are to:    

This document is aimed to help managers understand how to implement an IPM approach to manage for productive forest and plantation stands in coastal Oregon and Washington in the face of Swiss needle cast (SNC).

According to the Environmental Protection Agency, “Integrated Pest Management (IPM) is an effective and environmentally sensitive approach to pest management that relies on a combination of common-sense practices.  IPM programs use current, comprehensive information on the life cycles of pests and their interaction with the environment. This information, in combination with available pest control methods, is used to manage pest damage by the most economical means, and with the least possible hazard to people, property, and the environment.  IPM is not a single pest control method but, rather, a series of pest management evaluations, decisions and controls” (EPA IPM Factsheet).

Although some of the focus of IPM strategies is on reduced pesticide or fungicide use, particularly when these solutions are not economically viable, the feature common to all IPM strategies is that thresholds for action are set, which allow landowners to make decisions on how to best manage their resource in the face of disease and/or insect pressure using a variety of tools.

Silviculture of SNC: Research and Recommendations, Filip et al. 2000

1. Set Action Thresholds

Before making decisions about how manage for Swiss needle cast (SNC) or other disease or insect problems, it is important to set an action threshold, which is a point at which disease severity, growth losses or environmental conditions indicate that action must be taken.  The fungus that causes SNC, P. gaeumannii, is present throughout the range of Douglas-fir, but only causes significant disease or growth loss under certain conditions.  Therefore, the presence of the fungus alone is not sufficient to warrant management action.  Determining the level at which SNC represents an economic threat is critical to guiding management decisions for SNC.

  • Private landowners must work to set their own action thresholds, but can use the tools established by SNCC researchers and collaborators to make management decisions.
  • Some of the decisions that landowners can make include:
    • Whether or not to pre-commercially thin and what pre-commercial thinning options to consider
    • What species composition to plant on recently harvested sites with low, moderate or severe disease pressure
    • Which fertilization regime is most appropriate considering a site’s initial soil composition (nutrients and pH)
    • Whether or not growth losses are substantial enough to warrant a sanitation cut, salvage cut or other action
    • What Douglas-fir planting stock/seed source to use when planting Douglas-fir or other species on sites with low, moderate or severe disease pressure
  • Specific recommendations that pertain to each of these management decisions are described in the “Control” section below (step 4 of the IPM strategy), under: “General guidelines for active management.

2. Monitor, Identify & Quantify Pests

Heavily infected 2-yr old needlesSwiss needle cast (SNC) is not the only agent that causes chlorosis, needle loss or other damage to Douglas-fir.  The fungus that causes SNC is present throughout the range of Douglas-fir and only causes severe disease when conditions are beneficial to fungal growth and reproduction.  The following tools can help managers to verify that SNC is causing the symptoms observed in their stands and to gauge whether SNC represents an economic threat.

  • The annual aerial survey and permanent monitoring plot network provide an essential framework for assessing the severity and distribution of Swiss needle cast (SNC) in the Oregon Coast Range, and also help managers to track whether the epidemic area is expanding or symptom severity is changing over time.
  • It is important for landowners to collect foliage to accurately identify Phaeocryptopus gaeumannii, the causal agent of SNC.  The identification key can help managers to distinguish between P. gaeumannii and other common damage agents of Douglas-fir.
  • Qualitative evaluation of needle retention and detection of fungal fruiting bodies on young needles are appropriate starting points for land managers to determine whether or not they may be facing growth losses from SNC.  Some useful rules of thumb:
    • If, on average, ≥3 needle age classes remain on trees, growth losses from SNC are likely to be negligible; conversely, if < 3 needle age classes remain, it is likely that the stand is experiencing growth losses attributable to SNC.
    • If fungal fruiting bodies are detected on young needle age classes (1-2 years), it is probable that the infected trees are experiencing growth loss.
  • High-resolution (1: 100K) aerial survey maps compiled by the Forest Health Protection branch of the US Forest Service provide a means for landowners to qualitatively assess whether SNC may be impacting stands under their management based on present and past aerial survey data.  Aerial survey maps and GIS data are also available from the Oregon Department of Forestry.
  • The SNCC strongly recommends that management decisions are based on quantitative assessments of SNC growth impacts using the Stand Assessment Tool; qualitative measures described above give landowners an initial means to evaluate whether quantitative measurements are warranted.
  • ORGANON growth model adjustment is another tool that landowners can use to quantitatively assess disease impacts and growth losses based; for information on the ORGANON adjustment, contact Doug Maguire (541-737-4215) or Doug Mainwaring (541-737-8107) in the College of Forestry at Oregon State University.
  • In addition to monitoring for SNC, it is also recommended that landowners assess soil nutrient composition and pH to assess whether traditional nitrogen fertilization is likely to benefit stand growth, or whether calcium or alternative fertilization regimes might be more appropriate.
  • For management recommendations see the “Control” section below, under: “General guidelines for active management”.

3.  Take Preventative Measures

As a first line of pest control, IPM programs work to manage resources to prevent diseases or pests from becoming a threat.  The SNC epidemic in plantation forests of coastal Oregon and Washington was first detected in the late-1980s.  Since that time, aerial and ground surveys have been used to identify topographic and climatic features associated with severe disease.

  • Factors associated with severe disease, such as mild winter temperature, high spring and early-summer fog and precipitation, and low elevation valleys and coastal areas, have been used to build several independent foliage retention models to assess current and predicted future disease levels.
  • Although managers often have a long history with the lands they manage, the models and aerial survey maps can help managers to assess disease severity and risk, especially on newly acquired sites and on sites on which disease pressure is changing over time.
  • When planting after harvest, managers are able to use all of the available tools to manage sites to yield the healthiest and most productive stands possible.
  • Some management tools include: assessing soil nutrients and pH and using this information to select the most appropriate fertilization regime, reducing shrub competition, planting mixed-species to minimize potential disease losses, reducing the proportion of Douglas-fir on moderate and high severity sites, planting SNC-tolerant and locally-adapted seed stock, and thinning before crown closure.  Some tools can only be implemented early in rotation, while others can be used at any time.  These management tools are described in detail in the “Control” section below.

4. Control

When monitoring, identification, and quantification of disease impacts indicate that disease losses are significant enough to warrant specific management action, landowners are able to select the proper control methods for their situation.

General guidelines for active management:

  • Pre-commercial Thinning
    • PCT does not appear to impact needle retention or disease severity; therefore, standard PCT practices are recommended on all but the most severely impacted sites (on which the benefits of thinning may not be worth the cost of the operation); note that PCT does not solve disease problems, but confers the same relative growth benefits as PCT in the absence of disease.
    • It is important to thin from below, because larger Douglas-fir trees have demonstrated the ability to grow well in the face of disease pressure compared to smaller trees.
    • Thin early (prior to crown closure) to preserve crown length and foliage in the lower crown, which is frequently retained longer than foliage in the upper crown in SNC-diseased stands.
    • “D-minus rule”: At the SNCC Workshop in November 2010, Jon Wehage and Roger Van Dyke from Stimson Lumber presented a practical tool for use in PCT.  Depending on the severity of SNC in a stand, an established number of inches (1-3”) can be subtracted from the diameter of Douglas-fir trees to identify which trees should be cut or retained.  This type of rule is easy for thinning crews to implement, and helps address the fact that, on sites with moderate to severe SNC, Douglas-fir trees that are initially larger than other species at the time of PCT are frequently outcompeted in subsequent years.  Managers can select an appropriate deficit depending on the degree of SNC disease severity at a site.  It is important that quantitative measures are used to determine SNC severity and a suitable corresponding deficit, as stands that appear to have severe SNC symptoms may be experiencing only moderate growth impacts.
    • D-minus rule example:  If a decision were being made about whether to thin a Douglas-fir with a DBH of 6”or an adjacent western hemlock with a DBH of 4”, a D-minus 3” rule might be applied on a high-severity site. Example equation:  [Actual measure- deficit] = [6”- 3”] = 3". Implementing this diameter deficit, the Douglas-fir would be compared at 3” to the 4” western hemlock, and the Douglas-fir would be thinned and the hemlock retained.
  • Species Composition
    • Douglas-fir is the only tree species susceptible to SNC.
    • Mixed-species management can help to reduce volume loss on sites with moderate to high SNC severity; common alternate species planted in the Coast Range include western hemlock, Sitka spruce and red alder.
    • It is also important to be aware of some of the insect and disease problems of alternate species, for example:
      • Sitka spruce/white pine weevils cause damage to leaders of Sitka spruce
      • Sitka spruce and western hemlock are prone to wounding and root damage; wounds and large cut stumps provide an entrance for Annosus Root Rot (Heterobasidion annosum)
      • Bumper trees and other practices can be used to limit damage from thinning and other operations, minimizing these risks
    • Depending on management objectives, it is possible to plant pure stands or mixes of alternate species, or to retain a target proportion of Douglas-fir, for example:
      • Low severity site (needle retention 2.6-3.5 yrs): maintain large proportion Douglas-fir, but only use local or tolerant seed
      • Moderate severity (needle retention 1.5-2.6 yrs): reduce Douglas-fir to 50% of regeneration planting, use local or tolerant seed
      • High severity (needle retention < 1.5 yrs): reduce Douglas-fir to ≤ 20% of regeneration planting; use local or tolerant seed
    • Of course, it is also important to consider the relative timber value of these species, and what species are accepted by mills for processing; quantifying growth losses from SNC using the Stand Assessment Tool provides a means to make these decisions.
    • Species composition can also be altered through PCT, as described above (D-minus rule); this allows managers to alter stand composition after planting.
  • Fertilization regime
    • Fertilization experiments conducted by SNCC researchers have found that traditional nitrogen (urea) fertilization may not be appropriate under certain soil conditions, particularly on soils with:
      • High site indices (>160)
      • Already high soil nitrogen
      • Low calcium to nitrogen ratios
      • Low soil pH
    • SNC tends to be most severe close to the coast, where there is also high nitrogen composition; therefore, it may be inappropriate to fertilize with urea on sites with high risk of SNC and high soil N.
    • Fertilization research through the SNCC is still underway:
      • Preliminary results suggest that after adjusting for site and tree covariates, increases in volume production were marginally greater (~3.4% volume increase) with the urea (N) and lime (Ca) treatments compared to unfertilized controls.
      • These benefits varied across sites depending on initial soil condition, etc.
      • The other 5 fertilization treatments did not significantly impact volume growth compared to unfertilized controls.
      • Fertilizer treatments do not appear to significantly impact needle retention, but pseudothecia counts on sampled foliage will allow for the assessment of fertilization impacts on disease severity; there was a strong correlation between foliar nutrient concentration and needle retention.
  • Growth loss- time to cut your losses with sanitation or salvage cuts?
    • Under severe SNC conditions, it is possible that disease impacts will be so high that trees are unlikely to reach merchantable size, and landowners may elect to implement sanitation or salvage cuts to “cut their losses”.
    • It is strongly recommended that drastic management decisions of this kind are based on quantitative assessments of growth impacts using the Stand Assessment Tool and carefully considered cost-benefit analyses.
  • Use Improved & Locally Sourced Douglas-fir Planting Stock
    • Research has shown that there is heritability in SNC tolerance, and out-planting trials are underway to monitor the productivity of selected families.
    • For more information on this research, see the Tree Genetics, Resistance and Improvement section in Past Research Summaries on this website.
    • Data from the 3rd measurement of 25 year old DF progeny trials in the coast range strongly indicate the ability of some families to continue diameter growth even after years of substantial SNC impact.
    • For more information on the Northwest Tree Improvement Cooperative (NWTIC) and SNC-tolerant Douglas-fir seed stock, visit their website or contact the NWTIC Director, Keith Jayawickrama
    • Follow this link to the Oregon Department of Forestry webpage on established Douglas-fir seed zones for western Oregon.
  • Fungicidal Control
    • In plantation forests, the disease control benefits of fungicide application are short-lived and are not cost-effective
    • Five successive years of aerial chlorothalonil application temporarily reduced disease symptoms but did not achieve complete disease control; infection levels rapidly returned to pre-treatment levels when application ceased
    • Chlorothalonil (Bravo, Echo, Daconil) has been shown to effectively reduce infection levels in both plantation forests (ground and aerial application) and Christmas tree plantations, but fungicidal control is only economically viable in high-value Christmas tree plantations
    • Sulfur-based fungicides are slightly less effective than chlorothalonil in controlling infection, but are less toxic and have less deleterious impacts on non-target organisms


5.  Evaluate

  • Evaluation is important to assessing whether desired management objectives were met, and can also help to determine if modifications should be made to your Integrated Pest Management (IPM) program.
  • Although managers growing Douglas-fir in the Oregon and Washington Coast Range are likely to continue to confront losses from Swiss needle cast (SNC), the goal of the IPM strategy is to minimize these losses and to help landowners to make informed management decisions.
  • It can be difficult to quantify the success of management actions, especially when they are applied in combination, outside of the traditional scientific experimental framework.
  • For this reason, the SNCC has implemented scientific studies to quantify growth and disease impacts under specific silvicultural prescriptions, and has based the above management recommendations on the research findings; these studies have been reported in the SNCC Annual Reports and in scientific journals, and research summaries available on this website.
  • Some of the questions that can be asked to assess the efficacy of management prescriptions include:
    • What are the details of the strategy that was implemented?  Why were those specific decisions made and what resources were use to make those decisions?
    • Were the objectives of the SNC IPM strategy met?  Were disease-related growth losses minimized?
    • Were there any unintended consequences of the strategy that was implemented?
    • Are there additional strategies that can be used in the future to minimize SNC growth losses?
  • The SNCC is interested hearing your feedback.  If you or your organization has recommendations on how we can broaden our IPM strategy to include a larger range of management options, please contact us with your ideas.